The Builder type

A Builder is an efficient way to build lazy Texts. There
are several functions for constructing Builders, but only one to
inspect them: to extract any data, you have to turn them into lazy
Texts using toLazyText.

Internally, a Builder constructs a lazy Text by filling byte
arrays piece by piece. As each buffer is filled, it is 'popped'
off, to become a new chunk of the resulting lazy Text. All
this is hidden from the user of the Builder.